The Norwegian Earth System Model (NorESM) is a global, coupled model system for the physical climate system, which can be run with various degrees of interactions with biogeochemical processes in the earth system. NorESM is developed as a nationally coordinated effort in Norway, but important parts of the model code are imported from the Community Climate System Model (CCSM) and Community Earth System Model (CESM) projects operated at NCAR on behalf of UCAR in the USA.

The NorESM publications in this special issue address a range of NorESM versions. The first set of model versions delivered results to CMIP5. NorESM1-M is run concentration-driven for greenhouse gases (GHGs) and is based on CCSM4 (released 1 April 2010), while NorESM1-ME can be run emission-driven for GHGs and is based on CESM1 (released 1 July 2010). A low-resolution version, NorESM1-L, was developed mainly for paleo-climate simulations. New versions of NorESM are underway: NorESM1.X, where X indicates updates of the NorESM1 versions, and NorESM2, which is intended to contribute to CMIP6. Further versions will follow thereafter. NorESM includes the following: its own developed code for chemistry–aerosol–cloud–radiation interactions (CAM-Oslo) and enhancements of the dynamics/physics of the atmospheric module; alternative parameterization of surface turbulent fluxes; an isopycnic coordinate ocean model originating from the Miami Isopycnic Coordinate Ocean Model (MICOM) but developed further; and the HAMburg Ocean Carbon Cycle (HAMOCC) model developed at the Max Plank Institute for Meteorology, Hamburg and adapted to the isopycnic coordinate ocean model framework.

Papers developed for full validation (CMIP-DECK) or more specific evaluation of the NorESM versions and further developments of these are welcome in this special issue. Authors intending to contribute papers to this special issue should contact the coordinators (Mats Bentsen and Michael Schulz), e.g., to ensure the consistency of version names and numbers.